Method for handling heat-softenable batch material

ABSTRACT

A method provided for handling heat-softenable batch material prior to melting it. The batch components are mixed together and then mixed with liquid and formed into balls or pellets of substantially uniform size and shape. The pellets are then collected into a heat-exchange chamber through which hot gases are passed from a melting unit in which the pellets are to be heated to a heat-softened state. The pellets thereby are preheated prior to entering the melting unit to save considerably on energy requirements. A physical characteristic and specifically the depth of a portion of the batch being formed into the pellets is sensed, the depth being related to moisture content. The ratio of the batch material and liquid is accordingly regulated to achieve uniformity in pellet size, which is influenced by the moisture content. Size uniformity is important in maintaining relatively free flow of the hot gases through the pellets in the heat-exchange chamber.

This is a continuation, of application Ser. No. 049,865, filed June 18,1979 abandoned. Application Ser. No. 49,865 was a continuation ofapplication Ser. No. 809,595 filed on June 24, 1977 now abandoned.

This invention relates to a method for handling batch of heat-softenablematerial prior to being supplied to a melting unit.

It has been found to be advantageous to collect the products ofcombustion or hot gases over molten glass in a glass melting furnace orunit and to pass them in heat-exchange relationship with the batchmaterial being supplied to the melting furnace. The batch can thus bepreheated to elevated temperatures to save significant amounts of energysubsequently required to melt the batch. The exhaust gases otherwise aresimply expelled to the atmosphere in many instances with a considerablewaste of heat and energy.

Preferably, the heat-softenable batch material is in the form of ballsor pellets in the heat-exchange chamber through which the hot gases arepassed. However, it has been discovered that the pellet size must besubstantially uniform. Otherwise, pellets of varying sizes tend to nestand provide excessive restriction to the flow of the gases past thepellets in the chamber. It has also been discovered that pellet size isimportant in addition to uniformity. If the pellets are too small, againundue restriction to the flow of the hot gases results. If the pelletsare too large, their surface-to-weight ratio is accordingly reduced andthe heat transferred to them is accordingly decreased. Also, trappedmoisture in the larger pellets may turn to steam and cause the pelletsto explode. Specifically, it has been found that pellets of one-halfinch nominal diameter with a range from three-eighths inch tofive-eighths inch in diameter are the ultimate for obtaining maximumheat transfer from the hot exhaust gases to the pellets.

The pellets of the heat-softenable batch material preferably are made ina modified commercially-available pelletiser. The components of thebatch are mixed together and then supplied to the pelletiser. Duringtransportation to the pelletiser, the batch components tend to segregateso that the actual batch supplied to the pelletizer will vary, eventhough the final pellets produced and supplied to the melting furnace orunit average out so that the short variations are not material. However,the short variations in the batch components tend to affect thepellet-forming ability of the batch and the size of the pelletsproduced, other factors being constant. The feed rate of the batch tothe pelletiser will also vary and thereby also affect pellet forming andpellet size. Liquid, and specifically water, is also supplied to thepelletiser near the batch supply. With the batch component or quantityvariation, different size pellets will result when the water quantity isheld constant. However, it has been found that the water quantity, orthe ratio of the batch to the water, will also affect the pellet size,with more water resulting in larger pellets and less water resulting insmaller pellets, at least in most instances.

It has also been discovered that measuring a physical characteristic ofthe batch on the pelletizer during the formation of the pellets canresult in a forecast or prediction of pellet size so that the quantityof water or batch to water ratio can be changed to avoid an undesiredincrease or decrease in pellet size prior to its happening. Morespecifically, the depth of the batch material in the pelletizer atcertain portions thereof can be measured and the water flow changedaccordingly. An increased depth of the nuclei or seeds of the batchmaterial indicates that water content is higher, the water tending tocause the seeds to stick together more and thus build up higher.Consequently, the amount of water supplied to the pelletizer is reducedwhen the sensing device indicates that the batch depth has reached apredetermined value. The excess water would otherwise tend to make fewerbut larger diameter pellets, if not reduced. At the same time, if thereis too little water, the depth of the nuclei or seeds of the batchdecreases with the amount of water then being increased. The lesseramount of water otherwise would result in the individual final pelletsthereby being smaller but in greater quantity.

It is, therefore, a principal object of the invention to provide animproved method for handling heat-softenable batch material prior tosupplying it to a melting unit.

Another object of the invention is to provide a method for preheatingbatch material prior to supplying it to a melting unit by forming thebatch into pellets which are of a substantially uniform size and shape,and then supplying hot exhaust gases into heat-exchange relationshipwith the pellets.

A further object of the invention is to provide a method for producingpellets of a particulate batch material which are of substantiallyuniform size and shape.

Yet another object of the invention is to provide a method for producinguniformly-sized pellets by sensing a physical characteristic of batchmaterial from which the pellets are made in a pelletizer.

Many other objects and advantages of the invention will be apparent fromthe following detailed description of preferred embodiments thereof,reference being made to the accompanying drawings, in which:

FIG. 1 is a somewhat schematic view in elevation of overall apparatusfor handling heat-softenable batch material;

FIG. 2 is a front view in elevation of pelletizing apparatus shown inFIG. 1;

FIG. 3 is a top, plan view of the apparatus of FIG. 2;

FIG. 4 is an enlarged, diagrammatic view of a portion of the pelletizingapparatus; and

FIG. 5 is a diagrammatic view of controls for sensing batch material inthe pelletizing apparatus and for controlling the flow of water to theapparatus.

Referring to FIG. 1, particulate, heat-softenable batch material istransported to a supply hopper 10 and supplied to a pelletizer 12. Theparticulate batch material is formed into pellets which are dischargedonto a trough 14 having openings 16 (FIGS. 2 and 3) through whichsmaller or broken pellets can be separated. The pellets are supplied toa horizontal conveyor 18 and then carried up by a vertical conveyor 20to the top of a heat-exchange hopper 22 which forms a heat-exchangechamber. The pellets next move down a supply tube 24 to a feeder 26which carries the pellets into a melting unit or furnace 28.

Hot exhaust gases or products of combustion from the furnace 28 arecarried up an exhaust stack 30 to the bottom of the hopper 22. Theexhaust gases are then drawn through the hopper 22 by a blower 32 anddischarged. The heat-exchange hopper 22 is large enough that the exhaustgases passing therethrough will be at a low velocity and not carry someof the pellets out through the blower 32. A substantial portion of theheat in the exhaust gases is transferred to the pellets in theheat-exchange hopper 22 so that the pellets are at an elevatedtemperature when they enter the furnace 28. A substantial increase inefficiency of the furnace 28 is thereby achieved.

The size uniformity of the pellets themselves is very important. If thepellet size varies too much, the pellets tend to nest together in thehopper 22 and excessively restrict the flow of the exhaust gasestherethrough. However, if the pellets are of sufficiently uniform size,there will be sufficient voids among them that exhaust gases can passthrough without excessive impediment. The nominal diameter of thepellets is also important because pellets which are too small provideexcessive restriction to the flow of the exhaust gases. On the otherhand, if the pellets are too large, their surface-to-weight ratio islower and the heat transferred to them is decreased. Further, in thelarge pellets, moisture tends to be trapped therein and turned to steamby the exhaust gases, causing the pellets to explode. More specifically,by way of example, pellets having a nominal diameter of one-half inchwith a range of three-eighths to five-eighths inch have been found to bethe ultimate for obtaining maximum heat transfer from the exhaust gasesto the pellets in the heat-exchange hopper 22.

The pelletizer 12 is intended to form the particulate batch materialinto the one-half inch nominal diameter pellets. Unfortunately, thecomponents of the batch material supplied to the pelletizer 12 andspecifically to the supply hopper 10 tend to segregate duringtransportation. Such segregation is not deleterious to the operation ofthe furnace 28 since the components of the pellets supplied thereto willaverage out over a period of time. However, the short variations in thebatch components do affect the pellet-forming ability of the batchmaterial. In other words, variations in the components of the batchmaterial supplied to the pelletizer 12 will result in a change in pelletsize, with other factors maintained constant. The feed rate of the batchto the pelletizer will also vary and change the pellet-forming abilityand the pellet size with other factors being constant.

Liquid, and specifically water, is supplied to the pelletizer 12 and ithas been found that the water quantity or the ratio of the water to thebatch material will affect the pellet size. An increase in the amount ofwater or an increase in the ratio of the water to batch material resultsin larger pellets being produced, while less water results in smallerpellets, at least with most batch materials. Also, in accordance withthe invention, it has been found that certain physical characteristicsof the batch material on the pelletizer 12 can be sensed to control theflow of water or the ratio of water to batch material to maintain thepellet size in the desired range. More specifically, the depth of thebatch material or the pellets being formed at certain portions of thepelletizer can be measured, with the water flow then controlledaccordingly. An increased depth of the nuclei or seeds of the batchmaterial on which the pellets are formed indicates that the seeds aretending to stick together more and thus increase in depth. This occurswhen the amount of water or ratio of water to batch material increases.When the depth increases, the amount of water supplied to the pelletizeris then reduced because a continued excess of water otherwise wouldcause fewer but larger pellets to be formed. Also, when the depth of thenuclei or seeds is less, they tend to stick together to a lesser extent,indicating that the water content has decreased and that the pellet sizeaccordingly will be smaller. The amount of water is then increased toprevent this.

Referring to FIGS. 2-4, the pelletizer 12 includes a movable surface 34specifically formed by a rotatable member or disc, in this instance. Themovable surface can also take other forms, however, such as a drum or acone for producing the pellets. The disc 34 is rotatably carried on abearing housing 36 (FIG. 1) which is pivotally mounted on arms 38carried on an axle 40 which is mounted on a stand 42. The disc 34 ismoved or rotated by a suitable motor 44. An annual wall 46 surrounds therotatable member 34 with the pellets tumbling over this wall and down aspout 47 to the trough 14 when of the final size. An outer cleaning plow48 (FIGS. 2 and 3) and an inner cleaning plow 49 clean the surface ofthe rotatable member 34.

Batch from the supply hopper 10 is supplied to a lower central portionof the rotatable member 34, as indicated in FIG. 4, by a suitable feeder50. In this instance, the feeder 50 is shown as having a belt conveyor52 (FIG. 2) driven by a motor 54; however, other conveyors such asvibratory conveyors can be equally well employed. While the feeder isintended to supply a constant quantity of batch, as a practical matter,the feed rate of substantially any feeder is subject to some variation.This requires changes in the water supply even though the batchcomponents do not vary. In addition, water is supplied to a lowercentral portion of the rotatable member 34, at a portion thereof shownin FIG. 4, by a supply line or spout 56. With the rotatable member 34rotating in a clockwise direction, as shown in FIG. 4, the batch iscarried in generally elliptical paths as it moves up the surface, thesurface being maintained at a preset angle to the horizontal, such as45°, as determined by the position of the legs 38.

Actually, the wet batch moves in three rather distinct streams or pathsas it is carried up the moving surface and falls back. In the outer pathare seeds or nuclei of the batch on which the pellets form. In themiddle path are partially formed pellets having diameters in the rangeof one-fourth to three-eighths inch when pellets having a nominaldiameter of one-half inch are to be produced. In the inner path arefinished pellets which roll in a tight elliptical path until they tumbleover the annular wall 46.

As the seeds or nuclei form, the particulate batch material gathersthereon in continuous layers to gradually increase the diameters of thepartially formed pellets until the desired size is attained. As moistureor water is introduced to the agitated mass of particulate material, thecapillary force of the water and the mechanical force of the agitationof the particulate material against the moving surface causes packingand coalescing of the material into firm bodies.

The batch material in the outer stream and also, at least to someextent, in the middle stream, tends to stick together more when there ismore moisture of water in the batch, with the depth of the streamcorrespondingly increasing. When this depth reaches a predeterminedvalue, the water is cut back with the build-up of the batch materialaccordingly decreasing again. Otherwise, with the higher water content,the batch tends to agglomerate onto existing nuclei or seeds morereadily, rather than forming new seeds, with fewer or larger pelletsthereby resulting. Oppositely, with less moisture or water, theagglomeration tendency of the particulate batch material is decreasedwith more nuclei or seeds forming, which results in more but smallerpellets since there are more nuclei on which a given amount of batch canform, and there is a lesser tendency for the batch to agglomerate.

The water supply through the spout 56 to the moving surface 34 can becontrolled by the system shown diagrammatically in FIG. 5. Accordingly,water is supplied to the spout 56 through a first branch passage or line58 having a manually-controlled valve 60 therein. Water can also besupplied to the spout 56 through a second branch passage or line 62having a solenoid-operated valve 64 and a manually-controlled valve 65for adjustment. Water for both of the lines 58 and 62 can be suppliedthrough a suitable supply line 66. The flow of water through the line 58to the spout 56 is such as to be less than the amount needed to producethe desired size pellets on the pelletizer 12. However, the flow ofwater through both of the lines 58 and 62, when the valve 64 is open, isin excess of the amount needed for producing pellets of the desiredsize.

By way of example, with a typical batch material which is supplied tothe pelletizer 12 at the predetermined rate of 2000 pounds per hour, forexample, a water supply of forty gallons per hour may be required toproduce pellets of a given nominal diameter. However, for shortvariations in the batch components, the amount of water may need to bevaried from perhaps 35-45 gallons per hour in order to maintain thepellet size relatively constant. In that instance, the water flowthrough the first branch passage 58 can be set at 30 gallons per hour,below the minimum required. The supply of water through the secondbranch passage 62 can then be set at 20 gallons per hour. The combinedflow through both of the passages 58 and 62 will then be 50 gallons perhour, which is in excess of the maximum quantity of water required.Thus, liquid flow through the passage 58 is supplemented fromtime-to-time by flow through the passage 62 to obtain the pellets of thedesired nominal diameter.

The control of the water through the passages 58 and 62 is regulated bya suitable sensing device which senses a physical characteristic of theparticulate batch material on the surface 34. The sensing device cansense the water content, as previously discussed, and can do this bysensing the depth of the nuclei or partially formed pellets moving inthe outer or middle streams on the surface 34. In the specific exampleshown, the solenoid valve 64 is controlled through a timer 68 which,when energized, supplies power through contacts therein to the solenoidof the valve 64 for a predetermined period of time, such as fourseconds. Power to energize the timer, in turn, is controlled through aswitch 70. The switch 70 has an actuating stem 72 connected with an arm74 supporting a sensor or paddle 76. The arm 74, in turn, is pivotallysupported by an overhead bar 78 connected to a post 80 at one side ofthe pelletizer wall 46. The arm 74 is normally held against the stem 72by a spring 82 to keep the switch 70 open.

The paddle 76 is located near the annular wall 46 above an upper, outerportion of the surface 34 of the pelletizer. It preferably is in aposition to determine the depth of the seeds or nuclei in the outer pathof the batch material on the moving surface 34 but can also sense thedepth of the partially formed pellets. When the depth of the batchmaterial, whether seeds or pellets, reaches a predetermined amount orlevel, the paddle 76 is contacted and moved in a counterclockwisedirection, as viewed in FIG. 5. The batch material, as discussed before,reaches the predetermined depth when the water content increases andcauses it to stick together and build up. Consequently, when thiscondition occurs, it is desired to decrease the amount of water in thebatch or decrease the ratio of the water to batch. For this purpose,when the paddle 76 is moved, it pulls the actuating stem 72 of theswitch 70 outwardly to close the switch and energize the timer 68 forits predetermined period of time. When the timer is energized, it closesthe valve 64 and results in only the water from the line 58 beingsupplied to the spout 56. Each time the paddle 76 is moved, it resetsthe timer 68 so that the valve 64 remains closed until the paddle is nolonger contacted by the batch material for a period of time exceedingthe period set on the timer. With this arrangement, the water contentcan be maintained substantially constant in the batch so that thedesired nominal size of the pellets will be produced.

If desired, the sensor, or paddle, can be employed to control the flowof the batch material by the feeder 50. With the arrangement shown, themotor 54 can be a two-speed motor to drive the belt 52 at differentspeeds. If a vibrating feeder is employed, the rate of vibration can becontrolled for the same purpose. Thus, instead of increasing the flow ofwater, the batch feed can be decreased, and vice versa.

Different types of sensors other than the paddle can also be employed.Thus, the depth of the pellets can be sensed by an electric eye. Also,ultrasonic waves or microwaves can be employed for this purpose. Inaddition, the sensing device can directly measure the water content ofthe particulate batch material, such as by infrared rays.

Various modifications of the above-described embodiments of theinvention will be apparent to those skilled in the art, and it is to beunderstood that such modifications can be made without departing fromthe scope of the invention, if they are within the spirit and the tenorof the accompanying claims.

I claim:
 1. In a method of pelletizing particulate glass batch materialto form pellets having a select uniformity of size range and a selectnominal diameter range, comprising:(a) feeding under controlled flowconditions a supply of said particulate glass batch material onto aninclined rotating pelletizing disc, (b) feeding under controlled flowconditions a pelletizing water spray onto said particulate glass batchmaterial on said rotating disc while tumbling and rolling said batchmaterial on said disc, whereby pellets of particulate glass batchmaterial are formed, which roll and tumble over an annular wall of saidinclined rotating pelletizing disc, and (c) sensing glass batch materialat a select location on said rotating disc, the improvement comprising:where, in step (c), the depth of said material on said rotating disc issensed, and (d) regulating the flow of said batch material or water tosaid disc in response to said sensed depth of material to maintain aratio of water to said batch material on said disc to produce saidpellets having said select uniformity of size range and said selectnominal diameter range.
 2. The improvement of claim 1 wherein said flowof said water is regulated, with the proviso, however, that the feedingof said pelletizing water spray and said glass batch material iscontinuous.
 3. The improvement of claim 2 wherein the flow of said wateris regulated between a flow which is less than the amount needed toproduce said size and nominal diameter range and a flow which is inexcess of the amount needed for producing said size and nominal diameterrange.